(1) Field of the Invention
The invention relates to an actuation device for a shift-by-wire-actuated speed change gearbox, for example a gearbox or an automatic transmission with shift-by-wire actuation, according to the preamble of claim 1.
(2) Description of Related Art
Speed change gearboxes of automobiles are generally shifted or controlled with an actuating device arranged within the reach of the driver. Typically, actuating elements such as gear shift levers or selection levers are used, which are arranged, for example, between the front seats of the automobile or in other areas of the cockpit.
Ergonomic and safety reasons particularly require that shifting states which are currently not allowed, or the sequence of requested shifting operations are indicated to the driver via perceptible haptic signals in the form of corresponding shifting resistances and/or interlocks on the gear shift lever, similar to what a driver is used to, for example, from fully synchronized mechanical gearboxes having a rotation- and vehicle-speed-dependent synchronization interlock, or from conventional operation of an automatic transmission with its snap-in and shift interlocks.
It is therefore necessary to provide for the driver during actuation of the transmission clear haptic or tactile feedback about the actual shifting or operating state of the transmission or the success of the shifting operation.
With the electronic or shift-by-wire actuation of gearboxes, a mechanical coupling between the gear shift lever in the passenger compartment and the vehicle transmission in the engine compartment no longer exists. Instead, in a “shift-by-wire” gearbox, the shifting commands are transmitted from the actuating device to the vehicle gearbox by way of electric or electronic signals, followed by typically electro-hydraulic conversion of the switching commands on the gearbox. However, because of the missing mechanical link between the gear actuation assembly and the gear shift lever, the state of the gear, shift interlocks or prohibited shifting commands are no longer directly fed back to the state of the gear shift lever where they could be perceived by the driver.
When using shift-by-wire-controlled gearboxes, the driver is therefore unable to identify based on perceptibly blocked shifting positions on the gear shift lever that the lever positions, gear steps or shifting commands may not be allowable in the current driving state and can hence not be selected. Likewise, with shift-by-wire actuation, the execution by the transmission of the shifting commands from the driver is not fed back to the gear shift lever, so that the driver is unable to perceive haptically the course of events of the shifting operation in the same way he is used to, for example, with mechanically operated gearboxes with their snap-in and synchronization interlocks.
Depending on the state of the speed change gearbox to be operated and depending on other factors describing the state of the automobile—e.g., engine RPM, vehicle speed, clutch position and the like—it is therefore necessary for implementing the required haptic feedback in shift-by-wire-controlled transmissions to limit, delay or even entirely block the movement of the gear shift lever as well, depending on the state of the transmission, actively as well as under actuator control.
Only in this way can the driver, when he reaches for the gear shift lever, receive a haptic indication with a shift-by-wire-controlled transmission that the desired shifting operation—for example due to the actual speed of the automobile or due to a current operating state of the gearbox—is not permitted and therefore blocked. It can then also be prevented that shifting commands which can currently not be performed by the shift-by-wire transmission, but which are recognized by the transmission's electronic unit and are hence not transmitted from the actuating device to the transmission, can still be engaged on the gear shift lever.
Such actuating mechanism is also required on the gear shift lever if the driver is to experience with a shift-by-wire-controlled transmission the same haptic feedback as with a mechanically operated transmission—for example, with a manual gearbox with transfer linkage—, where engaging the individual gears on the gear shift lever generates on the gear shift lever corresponding perceptible counterforces, in particular rotation-speed or vehicle-speed-dependent counterforces.
As disclosed, for example, in DE 198 48 191 A1, attempts have been made in the state-of-the-art to implement a corresponding haptic with an actuating element for a speed change gearbox, wherein the actuating element is provided with an electronically controllable force-generating element or motion damper, which is controlled with a control device so that during actuation of the actuating element by the driver the counterforces which accompany the corresponding state changes in the speed change gearbox can be simulated on the actuating element.
For a realistic simulation of the haptic, in particular for a realistic emulation of the counterforces acting upon the gear shift lever, the control electronic of the operating lever must know at any time the state of the operating lever, i.e., its position and optionally angular velocity as well as the force actually applied on the operating lever by the driver. Conventional solutions require a first sensor which measures the position and optionally angular velocities of the operating lever, and an additional second sensor which measures the force generated by the user.
Safety requirements against system failure may make it necessary to implement these two sensors, which are essential in the state-of-the-art, in duplicate or triplicate. State-of-the-art systems therefore have substantial design complexity and correspondingly high costs due to the large number of required sensors.